Ion leaching and soil acidification in a forest haplic podzol: Effects of nitrogen application and clear-cutting

摘要

The main aim of this thesis was to investigate how small, frequently repeated applications of nitrogen affected (1) the leaching of K, Na, Ca, Mg, Mn, AlH(sup +), NH(sub 4)-N, NO(sub 3)-N, Cl and SO(sub 4)-S before and after clear-cutting and (2) the nutrient distribution in the plant-soil system (defined as soil plus above-ground tree biomass). Studies were conducted both in the field and in the laboratory. Two further aims of the thesis were (3) to evaluate two speciation methods for aluminium and (4) to improve a method for determining the molecular weight distribution of dissolved organic matter. Soil solution chemistry was measured in a haplic podzol in a Norway spruce (Picea abies) site in central Sweden that had received frequent low-dose applications of ammonium nitrate (30-120 kg N ha(sup -1) yr(sup -1)) and superphosphate (20-40 kg P ha(sup -1) every third year) during a long period (22 yr). The nitrogen load corresponded well with actual loads in central Europe. Before clear-cutting, fertilization increased concentrations of most ions in the soil solution. Total losses of NO(sub 3)-, Al and H+ increased with fertilization intensity; however, since fertilization increased tree growth, differences between the total losses of several other ions tended to decrease. After clear-cutting, nitrogen mineralization and nitrification increased, pH in the soil solution decreased, and losses of Mn and Al increased with N load. The concentration of SO(sub 4)(sup 2-) in soil solution decreased, probably owing to increased adsorption in the B horizon in response to the pH decrease. Biomass and soil sampling were carried out before the clear-cutting. Laboratory experiments largely confirmed results from the field experiment. It is important to evaluate the roles of surrounding ecosystems as well as the roles of different silvicultural systems. 50 refs, 2 figs, 1 tab